Increased activity of the complement system in cerebrospinal fluid of the patients with Non-HIV Cryptococcal meningitis

BACKGROUNDS Cryptococcal meningitis (CM) has been known to lead to significant morbidity and mortality. The relative contribution of the complement system in protection and pathogenesis during CM remains largely unknown. The purpose of this study was to evaluate the baseline complement component profiles in human cerebrospinal fluid (CSF) and plasma from non-HIV patients with CM, and therefore to provide insights of possible roles of the complement system in CM. METHODS CSF and blood samples from forty two CM patients not infected with HIV and thirteen non-CM control patients (Ctrl) were retrospectively selected and evaluated from the patients admitted to the hospital with a suspected diagnosis of CM. CSF and blood samples were collected at the admission. Enzyme-linked immunosorbent assay (ELISA) for complement components, cytokine IL-12 and western blot for C3 activation were performed on CSF and plasma samples. The levels of complement C1q, factor B (FB), mannose binding lectin (MBL), C2, C3, C4, C5, C4 binding protein (C4BP), Factor I (FI), Factor H (FH), sC5b-9 in CSF and plasma samples were compared. Pearson's correlation coefficients were calculated on variables between complement components and the levels of total protein in the CSF samples. RESULTS Our data demonstrated that the CSF levels of complement components of C1q, FB, MBL as well as complement pathway factors sC5b-9 and complement regulator FH were all elevated in patients with CM as compared to the controls, CSF C3 breakdown products iC3b were found in both CSF and plasma samples of the CM patients. A positive correlation was found between the levels of CSF protein and MBL, C1q or FB. CONCLUSIONS The activity of the complement system in CSF was increased in non-HIV patients with CM. C1q, MBL and FB are the important participants in the complement activation in CM. The relative contribution of each of the specific complement pathways and complement cascades in protection and inflammation resolution against CM warrant further investigation.